PROJECT SUMMARY Project I. Tumor-specific T cell state dynamics and heterogeneity in early tumorigenesis CD8 T cells are powerful components of the immune system that have the potential to selectively eradicate cancer cells, however, in most patients, tumors progress relentlessly despite the presence of tumor-specific CD8 T cells. We developed a genetic cancer mouse model that faithfully mirrors cancer development in patients and revealed that tumor-specific CD8 T cells enter a state of dysfunction early during tumorigenesis. These T cells exhibited the hallmarks of dysfunctional T cells from late-stage human tumors. Early after tumor initiation, T cell dysfunction was plastic, but at later times, became fixed. Breakthrough therapies (immune checkpoint blockade) have emerged to reverse T cell dysfunction but these strategies have only worked in a subset of patients and a subset of tumor types. The goal of Project I is to understand the co-evolutionary cancer cell, stromal and immune population dynamics that control T cell differentiation to different functional states and consequently, T cell sensitivity to immunotherapeutic interventions. We will leverage the power of clinically-relevant genetic cancer mouse models to dissect the complex interplay of cancer genomic evolution, immune and stromal cell population dynamics, and the molecular mechanisms controlling CD8 T cell differentiation using innovative single-cell transcriptional and epigenetic analytic tools and powerful mathematical modeling approaches. In Aim 1, we will define the chromatin states and/or transcription factor networks that mediate the transition between functional, plastic dysfunctional, and fixed dysfunctional T cell states. In Aim 2, we will characterize the mutational tumor antigen landscape, stromal and immune cell population dynamics, and TCR repertoire, and build and test a mathematical model to predict how these tumor parameters determine T cell functional states. In Aim 3 we will determine whether tumor-specific T cells in human solid tumors exist in heterogeneous functional states that predict responsiveness to immune checkpoint blockade therapy. By bringing together considerable expertise in cancer immune mouse modeling, computational methods, and clinical immune checkpoint blockade therapy, these approaches will provide new insights into T cell differentiation and could novel strategies to unleash the precise power of tumor-specific CD8 T cells for cancer immunotherapy.